Re: [PATCH v3 2/2] certs: Add support for using elliptic curve keys for signing modules

[Jarkko Sakkinen <jarkko@kernel.org>]

On Wed, Apr 21, 2021 at 03:43:19PM -0400, Stefan Berger wrote:
> Add support for using elliptic curve keys for signing modules. It uses
> a NIST P384 (secp384r1) key if the user chooses an elliptic curve key
> and will have ECDSA support built into the kernel.
> 
> Note: A developer choosing an ECDSA key for signing modules should still
> delete the signing key (rm certs/signing_key.*) when building an older
> version of a kernel that only supports RSA keys. Unless kbuild automati-
> cally detects and generates a new kernel module key, ECDSA-signed kernel
> modules will fail signature verification.
> 
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>

Looks good to me.

Acked-by: Jarkko Sakkinen <jarkko@kernel.org>

/Jarkko

> 
> ---
> v3:
>   - added missing OIDs for ECDSA signed hashes to pkcs7_sig_note_pkey_algo
>   - added recommendation to use string hash to Kconfig help text
> 
> v2:
>   - check for ECDSA key by id-ecPublicKey from output line
>     'Public Key Algorithm: id-ecPublicKey'.
> ---
>  certs/Kconfig                         | 26 ++++++++++++++++++++++++++
>  certs/Makefile                        |  9 +++++++++
>  crypto/asymmetric_keys/pkcs7_parser.c |  8 ++++++++
>  3 files changed, 43 insertions(+)
> 
> diff --git a/certs/Kconfig b/certs/Kconfig
> index 48675ad319db..d58f16c9f2d9 100644
> --- a/certs/Kconfig
> +++ b/certs/Kconfig
> @@ -15,6 +15,32 @@ config MODULE_SIG_KEY
>           then the kernel will automatically generate the private key and
>           certificate as described in Documentation/admin-guide/module-signing.rst
>  
> +choice
> +	prompt "Type of module signing key to be generated"
> +	default MODULE_SIG_KEY_TYPE_RSA
> +	help
> +	 The type of module signing key type to generate. This option
> +	 does not apply if a #PKCS11 URI is used.
> +
> +config MODULE_SIG_KEY_TYPE_RSA
> +	bool "RSA"
> +	depends on MODULE_SIG || IMA_APPRAISE_MODSIG
> +	help
> +	 Use an RSA key for module signing.
> +
> +config MODULE_SIG_KEY_TYPE_ECDSA
> +	bool "ECDSA"
> +	select CRYPTO_ECDSA
> +	depends on MODULE_SIG || IMA_APPRAISE_MODSIG
> +	help
> +	 Use an elliptic curve key (NIST P384) for module signing. Consider
> +	 using a strong hash like sha256 or sha384 for hashing modules.
> +
> +	 Note: Remove all ECDSA signing keys, e.g. certs/signing_key.pem,
> +	 when falling back to building Linux 5.11 and older kernels.
> +
> +endchoice
> +
>  config SYSTEM_TRUSTED_KEYRING
>  	bool "Provide system-wide ring of trusted keys"
>  	depends on KEYS
> diff --git a/certs/Makefile b/certs/Makefile
> index f64bc89ccbf1..c2fabc288550 100644
> --- a/certs/Makefile
> +++ b/certs/Makefile
> @@ -62,7 +62,15 @@ ifeq ($(CONFIG_MODULE_SIG_KEY),"certs/signing_key.pem")
>  
>  X509TEXT=$(shell openssl x509 -in $(CONFIG_MODULE_SIG_KEY) -text)
>  
> +# Support user changing key type
> +ifdef CONFIG_MODULE_SIG_KEY_TYPE_ECDSA
> +keytype_openssl = -newkey ec -pkeyopt ec_paramgen_curve:secp384r1
> +$(if $(findstring id-ecPublicKey,$(X509TEXT)),,$(shell rm -f $(CONFIG_MODULE_SIG_KEY)))
> +endif
> +
> +ifdef CONFIG_MODULE_SIG_KEY_TYPE_RSA
>  $(if $(findstring rsaEncryption,$(X509TEXT)),,$(shell rm -f $(CONFIG_MODULE_SIG_KEY)))
> +endif
>  
>  $(obj)/signing_key.pem: $(obj)/x509.genkey
>  	@$(kecho) "###"
> @@ -77,6 +85,7 @@ $(obj)/signing_key.pem: $(obj)/x509.genkey
>  		-batch -x509 -config $(obj)/x509.genkey \
>  		-outform PEM -out $(obj)/signing_key.pem \
>  		-keyout $(obj)/signing_key.pem \
> +		$(keytype_openssl) \
>  		$($(quiet)redirect_openssl)
>  	@$(kecho) "###"
>  	@$(kecho) "### Key pair generated."
> diff --git a/crypto/asymmetric_keys/pkcs7_parser.c b/crypto/asymmetric_keys/pkcs7_parser.c
> index 967329e0a07b..6592279d839a 100644
> --- a/crypto/asymmetric_keys/pkcs7_parser.c
> +++ b/crypto/asymmetric_keys/pkcs7_parser.c
> @@ -269,6 +269,14 @@ int pkcs7_sig_note_pkey_algo(void *context, size_t hdrlen,
>  		ctx->sinfo->sig->pkey_algo = "rsa";
>  		ctx->sinfo->sig->encoding = "pkcs1";
>  		break;
> +	case OID_id_ecdsa_with_sha1:
> +	case OID_id_ecdsa_with_sha224:
> +	case OID_id_ecdsa_with_sha256:
> +	case OID_id_ecdsa_with_sha384:
> +	case OID_id_ecdsa_with_sha512:
> +		ctx->sinfo->sig->pkey_algo = "ecdsa";
> +		ctx->sinfo->sig->encoding = "x962";
> +		break;
>  	default:
>  		printk("Unsupported pkey algo: %u\n", ctx->last_oid);
>  		return -ENOPKG;
> -- 
> 2.29.2
> 
>